1. How is Soil Formed?
Over many years, weathering and erosion will cause the formation of soil.
Soil is the loose, weathered material on the Earth’s surface in which plants can grow.
Soil forms as rock is broken down by weathering and mixes with other materials on the surface.

2. Soil Composition
Soil is constantly being formed wherever bedrock is exposed.
- Bedrock is the solid layer of
rock beneath the soil.
Soil is a mixture of rock particles, minerals, decayed organic material, air, and water.

3. Soil Composition and Texture
The decayed organic material in the soil is humus.
Humus is a dark-colored substance that forms as plant and animal remains decay.
Soil texture depends on the size of individual soil particles.
Soil texture is important for plant growth.
loam: rich fertile soil made of clay, sand, and silt

4. Soil Horizons
A soil horizon is a layer of soil that differs in color and texture from the layers above or below it.
A Horizon: Topsoil is a crumbly, dark brown soil that is a mixture of humus, clay, and other materials.
B Horizon: Subsoil usually consists of clay, and other particles washed down from the topsoil, but little humus.
C horizon: contains only partly weathered rock.
R horizon: bedrock/parent rock is a solid layer of rock under the soil.

5. Life in Soil
Some organisms mix the soil and make spaces in it for air and water.
Other soil organisms make humus, the material that makes soil fertile.
Humus forms through decomposition.
Fertile soil is rich in nutrients that plants need.
As plants shed leaves, they form a loose layer called litter.

6. With and Without Worms

7. Soil Conservation
Soil is one of Earth’s most valuable resources because everything that lives on the land depends directly or indirectly on soil.
Fertile soil is valuable because there is a limited supply.
- Less than 1/8th of the land on Earth
has soils well suited for farming.

8. Soil Damage and Loss
Soil can become exhausted, or lose its fertility (measure of how well soil supports plant growth).
Soil can also become lost to erosion by water and wind.
Water erosion can occur wherever soil is not protected by plant cover.
Wind erosion caused the Great Dust Bowl!!

9. The Dust Bowl
In the 1930s plowing removed the grass from the Great Plains and exposed the soil.
In times of drought, the topsoil quickly dried out, turned to dust, and blew away.
This event helped people appreciate the value of soil.

10. Soil Conservation
Soil Conservation is the management of soil to prevent its destruction.
Three ways that soil can be conserved include 1) contour plowing, 2) conservation plowing, and 3) crop rotation.

11. Contour Plowing
Contour plowing is the practice of plowing fields along the contours of a slope.
This helps slow the
runoff of excess rainfall
and prevents it from
washing the soil away.

12. Conservation Plowing
Conservation Plowing disturbs the soil and its plant cover as little as possible.
Dead weeds and stalks of the previous year’s crop are left in the ground to help return soil nutrients.

13. Crop Rotation
Soil can lose fertility if farmers grow the same crop in the same field year after year.
To prevent soil infertility, farmers will rotate crops to different fields each year (crop rotation).